An emergency room doctor who saw Sierra Jane for the seizure and a 107-degree fever late Aug. 24 wasn't sure what the cause was either and called other hospitals before the girl was flown to Denver.

There, a pediatric doctor at Rocky Mountain Hospital for Children racing to save Sierra Jane's life got the first inkling that she had bubonic plague. Dr. Jennifer Snow suspected the disease based on the girl's symptoms, a history of where she'd been, and an online journal's article on a teen with similar symptoms.

Dr. Wendi Drummond, a pediatric infectious disease specialist at the hospital, agreed and ordered a specific antibiotic for Sierra Jane while tests were run, later confirming their rare diagnosis.

It was the first bubonic plague case Snow and her colleagues had seen.

"I credit them for thinking outside the box," said Dr. Tracy Butler, medical director of the hospital's pediatric intensive unit.

The bubonic plague hasn't been confirmed in a human in Colorado since 2006, when four cases were reported.

Federal health officials say they are aware of two other confirmed and one probable case of plague in the U.S. so far this year - an average year. The other confirmed cases were in New Mexico and Oregon, and the probable case also was in Oregon. None died.

It's not clear why Colorado hasn't seen another human case until now, state public health veterinarian Elisabeth Lawaczeck said. Plague is generally transmitted to humans through the bites of infected fleas but also can be transmitted by direct contact with infected animals, including rodents, rabbits and pets.

Officials with the Centers for Disease Control and Prevention acknowledged that a series of frightening illnesses linked to insects and pests have been surfacing lately across the country, including mosquito-borne West Nile virus outbreaks in Texas and other states, deadly hantavirus cases linked to Yosemite National Park, and some scattered plague cases.

But with some of the illnesses - like plague - this is not an unusually bad year; it's just getting attention. And the number of cases of each disease is driven by different factors.

"I don't think there's a confluence of any particular set of factors" driving the recent illness reports, said Kiersten Kugeler, a CDC epidemiologist in Colorado who tracks plague reports.

In Sierra Jane's case, by the night of Aug. 25, the girl's heart rate was high, her blood pressure was low, and a swollen lymph node in her left groin was so painful it hurt to undergo the ultrasound that detected the enlarged node, Snow said.

Doctors say the girl could be discharged from the hospital within a week.

On Wednesday, Sierra Jane flashed a smile with two dimples as she faced reporters in a wheelchair, her pink-toed socks peeking out from the white blanket enveloping her as she held a brown teddy bear.

"She's just a fighter," said her mother, Darcy Downing.

Darcy Downing said her daughter may have been infected by insects near a dead squirrel she wanted to bury, even though Darcy had warned her daughter to leave it alone. She remembered catching her daughter near the squirrel with her sweat shirt on the ground. Her daughter later had the shirt tied around her torso, where doctors spotted insect bites.

The bubonic plague wiped out at least one-third of Europe in the 14th century. Today, it can be treated with antibiotics, but it's important to catch it early.

"If she had stayed home, she could've easily died within 24 to 48 hours from the shock of infection," Snow said.